1. Field of the Invention
Aspects of the present invention relate to an illuminating light source for a scanner module, to read information from an object, and an image scanning apparatus employing the scanner module.
2. Related Art
As shown in FIG. 1, a scanner module generally illuminates an object, e.g., a document disposed on a cover glass 3, with light from a light source 1. A scanner module generally forms an image with the light reflected from the document, through an imaging lens 5 and onto an image pickup device 7 (e.g. sensor). As shown in FIGS. 2 and 3, the amount of light picked-up from the image decreases from the center toward the edges of the image, due to the optical characteristics of the imaging lens 5.
As shown in FIG. 2, the amount of distributed light, i.e. the illumination, of the surface of a document is uniform across the document. Due to the optical characteristics of the imaging lens 5, the illumination of an image forming surface, of the image pickup device 7, is the highest in the center of the image forming surface and gradually decreases toward the edges thereof, due to the properties of the lens 5
The decrease in the amount of light focused through the edges of the lens 5 (reaching the edges of image pickup device 7) is represented as a function of an angle θ formed between an image reading unit (not shown) and the imaging lens 5. Generally, the decrease in the light intensity is proportional to cos 4θ. That is, as the angle θ becomes larger, the light amount is drastically decreased. Accordingly, the intensity of a signal inputted to the image pickup device 7 becomes weaker toward the edges, and the signal to noise ratio decreases. The decreased light amount causes a gradation difference between the center and the edges of an image.
To narrow the difference in the light amount, a conventional method, of decreasing the light amount of the center, is employed, as shown in FIG. 4. Referring to FIG. 4, the conventional illuminating light source includes: a lamp holder 10; a lamp 11, which is mounted in the lamp holder 10 and emits light; and a reflection plate 13, which is mounted in the lamp holder 10 and reflects incident light, so that the light emitted by the lamp 11 is directed in a predetermined direction. A non-reflective pattern 13a is formed in a predetermined region of the reflection plate 13, to decrease the light amount from the center of an image and to reduce the light amount difference. The non-reflective pattern 13a has a curvature that bocks more light from the center of an image than from the edges of an image.
If the illuminating light source is provided as shown in FIG. 4, a portion of the light emitted by the lamp 11 is blocked, thereby lowering light efficiency. A portion of the light, emitted to the non-reflective pattern 13a of the reflection plate 13, is absorbed by the non-reflective pattern 13a. Thus, the temperature of the reflection plate 13 increases, due to the absorption of thermal energy. Also, the non-reflective pattern 13a is printed in the reflection plate 13, thereby increasing production costs.